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Earthing of PV panels on roof ?


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Hi I am Roland , have a SMA 5kw Sunnyboy av40 with one string of 9x310 Engel PV panels facing east and another facing west 9x310! At present I am harvesting  on average 38kwh per day .

A friend who is a solar installer in Africa help me,or I help him ! 

Problem is i fall in the Coct area so we need to take the "Bush" out of the system !  and register the system !

The way I understand earthing is that a mounting rail in each array of panels (6 and 3 ) need to be earthed, a Schlettler mounting system  was used ,the two strings then connected , the earth wire then runs on the outside of the two sleeves taking the PV wires to the inverter. The earth then goes to the surge protector and then inverter to the earth rod outside the building. (Have been told that each panel needs to be earthed seperately with seperate wires ? ) what would be the thickness of the copper wire to the earth rod ?

According to Coct !!!

Thanks guys !

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 @flamegrilled can ask the Sparkie I referred to him, of what the wire size must be for earthing panels?

They did tell me, but it escapes me now - 6mm2 and 10mm2 where talked about.

What I did not know was that metal roofs must also earthed. 

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10 minutes ago, The Terrible Triplett said:

They did tell me, but it escapes me now - 6mm2 and 10mm2 where talked about.

It must not be smaller than whatever your PV wire is. That is all I know. So that would indicate at least 4mm^2 for most people.

15 minutes ago, The Terrible Triplett said:

What I did not know was that metal roofs must also earthed. 

It's good that you tell me.

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1 minute ago, plonkster said:

It must not be smaller than whatever your PV wire is.

My panel wires are 6mm2 and the earthing wire 10mm2 - so by that logic it is fine ... BUT ... I have never heard anything like that mentioned by anyone to date.

Even the house earth wire connecting to the main DB board is 10mm2.

The thicker the wire the better it solves the "potential" issues. :-)  (pun intended)

Google says: The ground conductor (earth wire) size is a determined by the rating (setting) of the up stream over current device.

So is lightning the up current device ito panels? :-) 

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16 minutes ago, The Terrible Triplett said:

Google says: The ground conductor (earth wire) size is a determined by the rating (setting) of the up stream over current device.

This is for ground faults. In residential setups we are used to having an RCD in place, and for ground faults to have very small margins (30mA), but the rules are a bit different in other places, where you rely on having a good ground so that a fault will cause a large enough current to flow... so large that it will trip an upstream overcurrent device. Now quite obviously... your earth wire has to be able to carry this current, otherwise the wire will burn up before the breaker trips.

In terms of PV then... the wire must be able to carry as much current as the fuses on your PV strings are rated for. Which is a bit weird, since we normally think of lightening rather than ground faults... but that is why the cable must be the same size of larger.

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The earthing conductor shall not be less than half of the current carrying conductor. That is for the general earth wire that runs to every point in your house and from the main pint of connection into your house.

In terms of bonding, which is what you are referring to, most will do with 6mm. Run a 6mm square cable from each string down to a earth point seperate from the earth connection at your inverter. On larger systems, to avoid running a million cables, you can calculate the bonding conductor to come down from the building and have a combiner on top to run all the strings to. When connecting to an earth spike, you need to be sure that the ground resistivity is within allowed parameters.  Notice should eb taken of the lighting protection system as well. If an isolated system is installed, this can`t be combined with you bonding. If a combined system is installed, the bonding becomes part of the lightning system. 

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Thanks for all the answers ! Being a retired garden boy  l am slightly confused !  Having watch this video: powerforum .co.za topic 2297 difference between various grounding toplogies.

I have two flats which are part of the main residence, they have been seperately wired with own internal meter,the power source is from "main residence" to get a Coc each unit had to have its own earth rod ! 

What I am now planning to do is to combine the earth wires from my two strings and take them straight to the nearest earth rod   which  belongs to one of the flats.The earth wire from surge breaker and inverter will go onto the earth rod which belongs to the other flat which is on the other side of the house....the earth wires will be 10mm2

Am I winning and will Coct like it ???

Thanks

Edited by Gatvol
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13 minutes ago, Gatvol said:

Am I winning and will Coct like it ???

If it was me, after all the money I spent, I would get a installation electrician in and ask him.

When our tests where done for the CoCT registration, the board failed due to a dormant unknown NE bonding issue.

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7 minutes ago, Gatvol said:

Just trying to sort out the things  that I "can" do before I have him do inspection !

Yes, it does make sense to do as much as we can.

But my recent experiences, I wasted my time, what took me hours took them moments, and I still had to pay for fixes.

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3 hours ago, anotherbrownbear said:

Run a 6mm square cable from each string down to a earth point seperate from the earth connection at your inverter.

This is also how I've understood PV module grounding and how I was initially planning on doing it, before people confused the heck out of me. So a few questions if I may:

1. If you sink your own earth spike, what kind of resistance are you looking for? Normally it would be < 30Ω ?

2. I don't suppose a single 1.2 meter copper spike is going to do it?

3. You've been to my place... it's actually a kind of wetland and there is a well about 2 meters deep that has water most of the year... :-)

I ask because I would much prefer to earth the roof and the PV panels to their own stake.

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19 minutes ago, plonkster said:

If you sink your own earth spike, what kind of resistance are you looking for? Normally it would be < 30Ω ?

Correct

 

20 minutes ago, plonkster said:

. I don't suppose a single 1.2 meter copper spike is going to do it?

Depends on type of soil

 

20 minutes ago, plonkster said:

You've been to my place... it's actually a kind of wetland and there is a well about 2 meters deep that has water most of the year... 🙂

It being wet definitely helps

 

The only way to properly check if your grounding is correct is to use an earth resistivity tester. I can`t rember the actual values out of my head now but will check and let you knw what it must be.

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I dont know which regualtions COCT is going to apply but I had a quick look at the latest SANS regulations.

WIth Cape town being in an area with less 6 flashes/km2/year you can leave the panels floating. Not that I would ever advice it, adding the bonding is such small price for peace of mind.

Local regs only refers to 4mm2 for mechincal strenght.

IEC 60364-7 specifies 6mm2 minimium for LPS

In Switserland 10 mm2 is set a requirement for LPS - so I guess that where someone picked that up from.

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12 minutes ago, Jaws said:

WIth Cape town being in an area with less 6 flashes/km2/year you can leave the panels floating. Not that I would ever advice it, adding the bonding is such small price for peace of mind. 

The quoted parts all seem to refer to <200Wp arrays. Most of us have somewhat bigger arrays... :-)

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